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CCIE Network engineer Detailed explanation of routing protocols IGRP and EIGRP

CCIE Network engineer must know

Detailed explanation of routing protocols IGRP and EIGRP

From their names alone, we can guess that there are many connections between them.

Get 100% accurate CCIE/ CCNP/CCNA/HCIE dumps in IELAB .

IGRP:

An internal gateway routing protocol designed by Cisco in the mid-1980s. Use combined user configuration metrics, including delay, bandwidth, reliability, and load. It has a high span within the same autonomous system and is suitable for complex networks. Cisco IOS allows router administrators to set the weight of IGRP network bandwidth, delay, reliability, and load to influence the calculation of metrics.

It is a Cisco proprietary routing protocol that provides routing functions in an autonomous system (AS: autonomous system). In the mid-1980s, the most commonly used internal routing protocol was Routing Information Protocol (RIP). Although RIP is very useful for implementing the routing of small or medium-sized interconnected networks of the same type, as the network continues to develop, its limitations are becoming more and more obvious. The practicality of Cisco routers and the powerful functionality of IGRP have led many small Internet organizations to replace RIP with IGRP. As early as the 1990s, Cisco introduced enhanced IGRP, which further improved the operational efficiency of IGRP.

For greater flexibility, IGRP supports multi-path routing services. In the Round Robin mode, two equal bandwidth lines can run a single communication stream. If one of the lines fails to transmit, the system will automatically switch to the other line. Multipath can be multipath lines that have different standards but still work.

IGRP maintains a set of timers and variables with time intervals. Including update timer, invalid timer, hold timer and clear timer. The update timer specifies how often route update messages should be sent. In IGRP, this value defaults to 90 seconds. The expiration timer specifies how long the router should wait before declaring the route invalid when there is no route update message for a particular route. In IGRP, this value defaults to three times the update period. The hold time variable specifies a hold-down period. In IGRP, this value defaults to three times the update period plus 10 seconds, or 280 seconds. Finally, the clear timer specifies the time the router waits before clearing the routing table. The default value of IGRP is seven times the route update cycle.

EIGRP:

CCIE Network engineer must know

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EIGRP: Enhanced Interior Gateway Routing Protocol is to enhance the interior gateway routing protocol. Also translated into enhanced internal gateway routing protocol. EIGRP is a private agreement of Cisco (it was publicized in 2013). EIGRP combines the link-state and distance vector routing protocol of Cisco’s proprietary protocol, using the dispersion correction algorithm (DUAL) to achieve rapid convergence, you can not send periodic routing update information to reduce bandwidth consumption.

EIGRP uses DUAL to achieve fast convergence. The router running EIGRP stores the neighbor’s routing table, so it can quickly adapt to changes in the network. If there is no suitable route in the local routing table and there is no suitable backup route in the topology table, EIGRP will query neighbors to find alternative routes. The query will continue to propagate until an alternative route is found or it is determined that there is no alternative route. Moreover, EIGRP sends partial updates instead of periodic updates, and only when the routing path or metric value changes. The update contains only the information of the changed link, not the entire routing table, which can reduce the bandwidth consumption. In addition, the propagation of these partial updates is automatically limited and only passed to the required router, so EIGRP consumes much less bandwidth than IGRP. This behavior is also different from the link-state routing protocol, which sends updates to all routers in the area.

CCIE Network engineer must know

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EIGRP uses a variety of parameters to calculate the metric value to the target network, including bandwidth (bandwidth), delay (relay), reliability (loading), and maximum transmission unit (MTU). These five parameters use K The value is expressed, that is, K1, K2, K3, K4, K5, so if the five K values ​​between the two EIGRP routers are different, it means that the two parties calculate the metric value differently; whether it is EIGRP or other protocols, you need to use When calculating the metric of bandwidth, only the outbound bandwidth of the interface is calculated, and the inbound direction of the interface is not counted. That is, on a link, the bandwidth of only one outbound interface is calculated, and the bandwidth of the inbound interface is ignored. of.

Five standards of EIGRP Metric:

 Bandwidth:

10 to the 7th power divided by the lowest bandwidth between the source and the target multiplied by 256 ).

Delay: The cumulative delay of the interface is multiplied by 256, and the unit is 10 microseconds.

Reliability: The value of the least reliable reliability between the source and destination according to keepalive.

Load: The value of the worst-case load between the source and destination according to the packet rate and interface configuration bandwidth.

Maximum transmission unit: The smallest MTU in the path. The MTU is included in the EIGRP routing update, but generally does not participate in the calculation of the EIGRP degree.

CCIE Network engineer must know

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